ERROR Your game session has expired, please log out and then log in again

After half an hour with Salve on LiveChat we worked out what the issue was - unsurprisingly, its Origin!

What you need to do is do all the steps I took in my previous post (although you probably dont need to reinstall BF4!) but you must clear the Origin cache living in your temp files.

There is a guide here : http://help.ea.com/en/article/clearing-your-origin-temporary-files/

Hopefully this works for anyone else with the same problem :-)